Why use estimation?

• We?estimate?to find approximations for difficult sums
• Or to check our answers are about the right size (right order of magnitude)

How to estimate

• We?round?numbers to something sensible before?calculating
• GENERAL RULE: 

  Round numbers to 1 significant figure

  • 7.8 ? 8
  • 18 ? 20
  • 3.65 × 10-4 ? 4 × 10-4
  • 1080 ? 1000

   

• EXCEPTIONS:It can be more sensible (or easier) to round to something convenient
  • 16.2 ? 15
  • 9.1 ? 10
  • 1180 ? 1200

   

It wouldn’t usually make sense to round a number to zero

• FRACTIONS get bigger when the top is bigger and/or the bottom is smaller and vice versa

Worked Example

轉載自savemyexam